Safety circuits for electronic apparatus



G GAGE 2,281,572

.n SAFETY CIRCUITS FOR `ELECTRONIC APPARATUS f- Filed sept. 12, 1940 y, ,Ili

UNITED STATES PATENT OFFICE SAFETY CIRCUITS FOR ELECTRONIC APPARATUS 'Edward G. Gage, Brooklyn, N. Y., assigner, by direct and mesne assignments, of two-thirds to Leon Uttinger, New York, N. Y.

Application September 12, 1940, Serial No. 356,460

3 Claims.

The invention relates to a safety system of electrical distribution in the operation of electronic apparatus to allow of safe handling of circuits supplying dangerous voltage and current for the operation of such apparatus, for exam.

ple, cathode ray tubes, Xray tubes, gaseous discharge and luminescent tubes, thermionic ampliers and the like.

The invention has for an object to provide a multiple path circuit for safety purposes, each branch including rectifying means and the paths being distributed in such a manner that each individual path may be contacted by the human body with safety; and at points in the circuit where the multiple paths are combined, such as 1 at the terminal of an electrode, to protect such separately and remotely controlled, instead of drawing the supply of current from a high voltage source common thereto, as is the standard practice.

Other and ancillary objects will hereinafter appear.

These objects are attained by dividing a dangerous current path or circuit into a plurality of parallel paths, and by insert-ing unilateral means such as a rectier in each path externally of the electronic device to be operated. Such an arrangement allows of contact with safety by the human body with any individual conductor, since the rectier inserted therein provides a one-way path and prevents the combined current from the remaining paths from returning through the body when such individual conductor is contacted thereby, as more particularly set forth in my copending application, Serial $337,806. The current in each path is limited to a safe value. which may be insuicient individually to operate the thermionic or other devices, but when combined with the currents in the remaining paths, as at a point close to an electrode of the device, the required current is secured. This point or portion of the circuit is protected by shielding, the required operating current and voltage being provided at the electrode while at the same time all circuits are made Safe to handle,

In the aforesaid prior applica- 55- tion, such shielding was not required as the rectifying means were located within the envelope of the electronic device, which envelope thus provided a shield.

To protect further the operator from dangerous voltages and currents, all variable circuits, that is to say, all circuits which supply current to the dangerous electrodes or elements of the device operated and requiring adjustment, are remotely controlled from the primary circuit of a separate transformer for each circuit and its electrode. The secondary of a transformer may supply alternating current directly to an electrode of the device, or it may feed a filter circuit including rectifying means for supplying direct current to the electrode. Such secondary of a transformer will thus be electrically insulated from its primary; or it may be additionally insulated, if required, from said primary. The controlling circuit, therefore, including the necessary adjustable resistanc-es or impedances, may be handled with safety at a distance from the apparatus.

In the practical application of my invention, I have found that the standard method of operating a cathode ray tube by drawing the voltage, which supplies the various electrodes from a common high-voltage source, by means of a potentiometer or so-called ubleeder circuits, has the disadvantage, especially in apparatus with critical adjustments such as a television set, of causing the control circuit of one electrode to interfere with a previous adjustment of another electrode circuit. This is due to the fact that the supply of high voltage from the common source is limited by resistance, and cannot provide suillclont current to one electrode without robbing some other electrode of current. This effect becomes very noticeable and objectionable when thc beam shift, for example, is varied. and a previous setting of focus or brilliance is upset. Not only does the standard system possess this defect but, in addition, because of the fact that a common source of high voltage is used, such a source must of necessity supply sufficient voltage and current for operating all of the electrodes of the device. Such current is therefore of a magnitudo as to be dangerous if its circuit be contacted by the human body. Furthermore, such a common source of high voltage requires that cach control shall be directly connected to the high-voltage source in close proximity thereto, thereby adding to the danger through a possible Hach-over, since it is obviously impracticable to operate such high voltages directly by remote control.

These disadvantages are obviated in the novel system shown in the accompanying drawing, wherein:

Fig. 1 is a schematic diagram illustrating a cathode ray tube operating at a dangerous voltage and current, but arranged for safe handling in accordance with my invention.

Fig. 2 is a fragmentary view of a similar arrangement and shows a modification in the supply for the second anode of the cathode ray tube.

Fig. 3 is a fragmentary view of a portion of a control circuit.

Referring to the drawing, more particularly to Fig. 1 thereof, I0 designates a source of current voltage, for example, alternating current, which may, for convenience, have a frequency oi 60 cycles, the same being designed for operation of the cathode ray tube II as one device to which my invention is applicable.

Tube II comprises the filament element or cathode I2, grid I3, first anode I4, second anode I5, and deecting members I6 and Il.

The cathode I2 is energized from the transformer 20, one terminal of the former being grounded as at 2|, or a metallic return (not shown) may be utilized. Transformer is connected to the source of supply I0 through a means for varying the power supply, for example, an adjustable resistor 22. Similarly, through resistors 23 and 24 power is supplied respectively to the grid I3 and rst anode I4, there being interposed, however, between the transformers 25 and 25, respectively, for supplying power to the respective elements, thermionic rectiers 21 and 28. Suitable iilter means 29 and 3D may also be included in the circuits beyond said rectifiers.

In the case of the second anode I5 which 0perates at a dangerous voltage and current, provision is made for providing a plurality of paths for the current supplied thereto, each being of a substantially like voltage and safe current. Thus, the transformer for this circuit has its primary connected to the source of supply I0 through the adjustable resistor 36, but a plurality of secondaries 31, 38, 39, and are provided, the same embodying a resistance sufciently high to limit the currents to safe values,

approximately 5 milliarnperes, for example, as set forth in my copending applications, Serial #330,636 and #337,806. Each secondary winding, which may either have a concentrated resistance included in series therewith or which may consist of a high resistance wire such as Nichrome, is connected to a corresponding thermionic rectifier 4I, 42, 43, and 44, and the outputs from the cathodes of these rectifiers are recombined and connected then to the said sccond anode, preferably through the filter means 45.

By this expedient, the circuits to and including the anodes of said rectiers may be safely contacted; and where the output circuits are combined. this portion is enclosed or shielded by a suitable casing 46 as of insulating material, the apparatus being designed in actual practice in a manner such that the output portion and/ or casing located in immediate proximity to the said cathode ray tube II or made a part thereof. Of course, the supply circuit t0 the iirst anode I4 may be similarly safeguarded should the voltage and current of such circuit be of a dangerous value.

The deflecting members I6 and I1 are connected to the source of supply I0 through corresponding rectiiiers 50 and 5I, respectively, and the transformers 52 and 53 whose respective primaries have included in circuit the corresponding resistors 54 and 55. Filter means 56 and 5l are also included in the respective circuits to the said deflecting members beyond the rectiers thereof. As the aforesaid resistors 54 and 55, as well as the resistors 22, 23, 24, and 36 are connected only in. the primary portion of the different operating circuits, said resistors may be 1ocated at a remote point as no portion of any of the respective primary circuits will be at a dangerous voltage or current; and, of course, these primary circuit portions may be further safeguarded, if required, by providing suitable insulation (not shown) between the primary and secondary portions of the respective transformers.

In Fig. 2 a modication is set forth in the means for safeguarding the power supply t0 the second anode BD of the cathode ray tube 6I. In this embodiment, the rectifying means are all combined Within a single envelope 62 and em body a plurality of anodes 63 which are energized from the individual secondaries 64 oi the transformer 55. A cathode 66 is common to these anodes 63 and is connected to the second anode preferably through the filter means 61. The operation of the tube is otherwise similar to that indicated in the embodiment shown in Fig. 1.

In place of the resistors for controlling remotely the power supplied to the circuits for operating the different elements of the cathode ray tube, it will be understood, reference being had to Fig. 3 of the drawing, that a resistor or resistors may be replaced by an adjustable impedance 'IIJ which is to be included in the primary circuit of a transformer, for example, of the transformer 1I.

I claim:

1. The combination with a source of electric current supply and unilateral means including a plurality of anodes and a cathodic portion operating at a dangerous voltage and current; of means, interposed between the said source of current supply and the said unilateral means, for separating the supply into a plurality of independent sources of dangerous voltage and corresponding paths to the respective anodes, each path including resistance permanently located in series with the respective sources of dangerous voltage such that all exposed parts of a path lie between a resistance and the unilateral means, said resistance being of such high magnitude that upon establishment of a closed circuit through said exposed parts and the human body the current in the particular path contacted is reduced by said resistance therein to a safe value, and a work circuit in series with a cathodic portion of the unilateral device, together with means for preventing electrical contact of the human body with exposed portions of the work circuit.

2. The combination with a source of electric current supply and unilateral means including a plurality of anodes and a cathodic portion operating at a dangerous voltage and current; of means, interposed between thesaid source of current supply and the said unilateral means, for separating the supply into a plurality of independent sources of dangerous voltage and corresponding paths to the respective anodes. each path including resistance permanently located in series with the respective sources of dangerous voltage such that all exposed parts of a path lie between a resistance and the unilateral means, said resistance being of such high magnitude that upon establishment of a closed circuit through said exposed parts and the human body the current in the particular path contacted is reduced by said resistance therein to a safe value, and a grounded work circuit in series with a cathodic portion of the unilateral device, together With means for preventing electrica1 Contact of the human body with exposed portions of the Work circuit.

3. The combination with a source of electric current supply and unilateral means including a plurality of anodes and a cathodic portion operating at a dangerous voltage and current; of means, interposed between the said source of current supply and the said unilateral means, for separating the supply into a plurality of independent sources of dangerous voltage and corresponding paths to the respective anodes, each path including resistance permanently located in series with the respective sources of dangerous voltage such that all exposed parts of a path lie between a resistance and the unilateral means. said resistance being of such high magnitude that upon establishment of a closed circuit through said exposed parts and the human body the current in the particular path contacted is reduced by said resistance therein to a safe value, and a cathode ray tube having an anode connected in series with the cathodic portion of the unilateral means, the cathode of said tube being grounded and the tube being located in close proximity to the unilateral means, together with means for preventing electrical contact of the human body with the circuit intermediate said unilateral means and said tube.

EDWARD G. GAGE. 

